Radiation detector comprising photodiodes and scintillators

ABSTRACT

The invention relates to a radiation detector, having a photodiode arrangement, a number of scintillators ( 4 ), and a reflector part ( 5 ) having a number of compartments ( 12 ) corresponding to the number of scintillators ( 4 ), which receive the scintillators ( 4 ) in such a way that the scintillators ( 4 ) are surrounded by walls ( 9, 10, 11 ) of the compartments ( 12 ) with the exception of their side respectively facing the photodiode arrangement.

[0001] The invention relates to a radiation detector, having a number ofscintillators which emit light when radiation to be detected impinges,which light is detected by photodiodes of a photodiode arrangement.

[0002] Such radiation detectors are used in computer tomographs, forexample. If X-ray quanta impinge on the scintillators, which arecomposed of a suitable luminescent material, for example luminescentceramic, the X-ray quanta are converted into light quanta. For theirpart, the light quanta are converted by the photodiodes into an electriccurrent corresponding to the intensity of the light, which current isamplified by means of an electronic unit and converted into digital datawhich are processed to form X-ray images by means of a computerassociated with the computer tomograph.

[0003] In order to obtain a maximum light yield on the photodiode, thescintillators composed of an optically transparent or translucentluminescent material are surrounded by an optically reflective materialon all sides except on their side facing the photodiode arrangement.

[0004] The scintillators are usually assigned a scattered radiationcollimator whose collimator plates are oriented to the focus of an X-raysource interacting with the radiation detector, so that essentially onlyX-ray radiation emerging from the X-ray source can pass to thescintillators, while the scattered radiation produced when carrying outan examination in the object under examination is at least essentiallykept away from the scintillators.

[0005] In a known radiation detector of modular construction for acomputer tomograph, each module has a photodiode arrangement with anumber of photodiodes which are each assigned a scintillator. In thiscase, the scintillators are not separate elements since this would makeit more difficult, if not impossible, to effect the exact positioning ofthe scintillators relative to the photodiodes.

[0006] What is used as a basis is a scintillator part whose length andwidth have a certain oversize relative to the length and width of thephotodiode arrangement.

[0007] This scintillator part is encapsulated at periphery and top sidewith a reflector coating, e.g. epoxy resin filled with titanium oxide,which serves as optical reflector. In this case, a defined layerthickness is ensured at the periphery by special casting molds. At thetop side, a defined layer thickness is ensured by mechanical processingin a special apparatus.

[0008] Afterward, the scintillator part is positioned on the photodiodearrangement by means of a special apparatus and adhesively bonded tosaid arrangement, in which case said apparatus can be removed again onlyafter the adhesive bonding has cured.

[0009] The elements thus produced are laterally trimmed on specialhigh-precision abrasive cutting machines and the scintillator element isslotted in such a way that each photodiode of the photodiode arrangementis assigned a scintillator. In this case, particular attention must bepaid to the slot depth in order to avoid damage to the photodiodes.So-called septa, for example aluminum foils coated on both sides, areadhesively bonded into the slots bounding the scintillators. The trimmedareas of the scintillator part are likewise bonded to septa.

[0010] Another manufacturing concept is based on adhesively bonding ineach case a scintillator and a photodiode to one another and assemblinga large number of such detector elements to form a radiation detector,it being possible in this case, too, to combine a plurality of detectorelements to form detector modules.

[0011] If the intention is to use a scattered radiation collimator, inboth manufacturing concepts it is complicated and difficult to positionthe scattered radiation collimator before the adhesive bonding to theradiation detector or detector modules relative to the latter in therequired manner. Therefore, complicated apparatuses are used in whichthe scattered radiation collimator and the radiation detector or thedetector module must remain until the adhesive bonding has cured.

[0012] The invention is based on the object of designing a radiationdetector of the type mentioned in the introduction in such a way that itcan be produced in a simple and uncomplicated manner.

[0013] According to the invention, this object is achieved by means ofthe subject matter of patent claim 1.

[0014] In the case of the invention, then, the reflector part not onlyrenders superfluous the septa required in the prior art and the coatingwith reflector coating, but additionally ensures that the scintillatorsassume defined positions relative to one another and relative to thephotodiodes of the photodiode arrangement.

[0015] Consequently, the processing of the scintillators is restrictedto tailoring them to the dimensions corresponding to the compartments inorder that they can be inserted into the compartments of the reflectorpart, where they are fixed by adhesive bonding in accordance with onevariant of the invention. As already mentioned, then, potting withreflector coating is not necessary, with the result that the expensivecasting molds required for this can be obviated. Moreover, there is noneed for expensive special machines for processing the scintillators.Furthermore, the slotting operations required in the prior art and theassociated risk of damaging photodiodes of the photodiode arrangementare obviated. Finally, as mentioned, septa are not required, whichrenders superfluous the production and handling of these sensitiveadditional parts.

[0016] It thus becomes clear that the radiation detector according tothe invention can be produced in a significantly simpler, lesscomplicated and thus more cost-effective manner than in the prior art.

[0017] In accordance with one preferred embodiment of the invention, thereflector part is of one-part design, for example as an injection-moldedor die-cast part, which is preferably produced from plastic, inparticular a plastic containing an optically reflective filler. Byvirtue of such a design of the reflector part, the latter and thus theradiation detector overall can be produced once again in a simpler andmore cost-effective manner.

[0018] A further preferred embodiment of the invention provides for thereflector part and the photodiode arrangement to have centering meanswhich interact with one another and which, in the case of thearrangement of the reflector part in front of the photodiodearrangement, ensure that the scintillators are arranged opposite therespectively associated photodiode. This measure further simplifies theproduction of the radiation detector according to the invention, sinceno complicated measures or apparatuses are required for ensuring therequired defined position of reflector part and photodiode arrangementrelative to one another.

[0019] If, in accordance with one variant of the invention, theradiation detector has a scattered radiation collimator with collimatorplates which is arranged in front of the reflector part, one embodimentof the invention provides for the reflector part and the scatteredradiation collimator to have centering means which interact with oneanother and which, in the case of the arrangement of the scatteredradiation collimator in front of the reflector part, ensure that thecollimator plates of the scattered radiation collimator are aligned withwalls of the reflector part which bound the compartments. This measureensures, in a simple manner, in particular without complicatedapparatuses, that the scattered radiation collimator and the reflectorpart are positioned correctly relative to one another.

[0020] One embodiment of the invention provides for the radiationdetector to be composed of a plurality of modules, each of whichcomprises a reflector part with scintillators and a photodiodearrangement, in which case each module can be assigned a scatteredradiation collimator.

[0021] An exemplary embodiment of the invention is illustrated in theaccompanying diagrammatic drawings, in which:

[0022]FIG. 1 shows a radiation detector according to the invention inthe form of an exploded drawing,

[0023]FIG. 2 shows the reflector part of the radiation detector inaccordance with FIG. 1 in a perspective view,

[0024]FIG. 3 shows a section along the line III-III in FIG. 2,

[0025]FIG. 4 shows a modularly constructed radiation detector accordingto the invention, and

[0026]FIGS. 5 and 6 show, in a partial illustration analogous to FIG. 2,a variant of the manufacture of the radiation detector according to theinvention.

[0027] As can be seen in FIG. 1, the exemplary embodiment of a radiationdetector according to the invention which is illustrated in FIGS. 1 to 3has, as essential elements, a photodiode arrangement 1 with photodiodes3 fitted on a substrate 2, a reflector part 5 containing scintillators 4and a scattered radiation collimator 6 with collimator plates 8 fittedbetween two side parts 7.

[0028] As can be seen from FIG. 2 in conjunction with FIG. 3, thereflector part 5 has a base plate 9, on which a frame-shaped boundarywall 10 is fitted.

[0029] The space surrounded by the boundary wall 10 is subdivided into anumber of compartments, one of which is provided with the referencesymbol 12, by partitions 11 running parallel to one another and parallelto two mutually opposite sections of the boundary wall 10.

[0030] The compartments 12 each receive a rod-shaped scintillator 4which is adhesively bonded into the respective compartment 12.

[0031] The dimensions of the scintillators 4 are coordinated with thecompartments in such a way that said scintillators completely fill saidcompartments.

[0032] In the case of FIGS. 2 and 3, only some of the compartments 12contain scintillators 4, in order to be able to illustrate theconfiguration of the compartments 12. It is understood, however, thatall the compartments 12 of the reflector part 5 contain scintillators 4in the assembled state.

[0033] It thus becomes clear that the individual scintillators 4, exceptat their side facing the photodiode arrangement 1, are surrounded bywalls of the reflector part 5, whether by the base plate 9, or by theboundary wall 10 or by the partitions 11.

[0034] Since the reflector part 5, which is designed as an injectionmolded or die cast part, is formed from an optically reflectivematerial, from epoxy resin treated with titanium oxide in the case ofthe exemplary embodiment described, it further becomes clear that thereflector part 5 takes over the functions which are performed by thesepta and the covering with reflector coating in the case of the priorart.

[0035] In order to ensure that the reflector part 5 containing thescintillators 4 and the photodiode arrangement 1, when joined togetherto form a unit, which can be done by adhesive bonding, for example,assume a defined position relative to one another in which the freesides of the scintillators 4, said free sides facing the photodiodearrangement 1, are arranged opposite the photodiode of the photodiodearrangement 1 which is assigned to the respective scintillator 4, insuch a way that the active areas of the photodiodes are congruent withthe free sides of the scintillators 4, the photodiode arrangement andthe reflector part 5 are provided with centering means which interactwith one another.

[0036] In the case of the exemplary embodiment described, these are pins13 which are fitted at the edge of the reflector part 5 and engage incorresponding openings 14 of the photodiode arrangement 1.

[0037] In order also to ensure a correct position of the scatteredradiation collimator 6 relative to the reflector part 5 with thescintillators, the reflector part 5 and the scattered radiationcollimator 6 are also provided with centering means which interact withone another, pins 15 fitted on the scattered radiation collimator 6being involved which interact with openings 16 provided on the reflectorpart 5 and ensure that the collimator plates 8 of the scatteredradiation collimator 6 are aligned with the partitions 11 of thereflector part 5.

[0038] As can be seen from FIG. 4, it is possible for a radiationdetector according to the invention to be composed of a plurality ofmodules, each of which has a reflector part with scintillators, aphotodiode arrangement and, if required, a scattered radiationcollimator. Such a subdivision into modules affords the advantage, forexample, that the individual modules are easy to handle.

[0039] In the case of the exemplary embodiments described therectangular photodiodes 3 are subdivided into, for example, squarephotodiode segments 17. Such a subdivision may be expedient, but is notabsolutely necessary.

[0040] The construction of the centering means described in connectionwith the exemplary embodiments is to be understood as only by way ofexample. The centering means can be embodied differently.

[0041] As an alternative to the procedure provided in the case of theexemplary embodiment in accordance with FIGS. 1 to 3, namely ofadhesively bonding separate rod-shaped scintillators 4 into thecompartments 12 of the reflector part 5, it may also be provided withinthe scope of the invention, in accordance with FIGS. 5 and 6, thatfirstly a scintillator blank 18 is produced from a plate of scintillatormaterial by the plate being structured by slots in such a way that thescintillator blank 18 comprises a relatively thin base plate 19 withrod-shaped scintillators 4 situated thereon and is configured in such away that it represents as it were the negative of the reflector part 5.This scintillator blank 18 is inserted into the reflector part 5 in sucha way that a scintillator 4 is situated in each of the compartments 12,and is adhesively bonded to the reflector part 5 in such a way thatthere is an adhesive bond between each of the scintillators 4 situatedon the base plate 19 and the respectively corresponding compartment 12of the reflector part 5. After adhesive bonding has been effected, thebase plate 19 is removed by material-removing machining, e.g. grinding,so that all that remains of the scintillator blank 18 are thescintillators 4 adhesively bonded to the compartments 12 of thereflector part 5.

[0042] The radiation detector according to the invention in accordancewith the exemplary embodiments is provided for computer tomography.However, radiation detectors according to the invention can be used ingeneral X ray technology and also for the detection of ionizingradiation whose wavelength range lies outside the length rangecharacteristic of X-ray radiation.

1. A radiation detector, having a number of scintillators which emit light when radiation to be detected impinges, which light is detected by photodiodes of a photodiode arrangement, and a reflector part having a number of compartments corresponding to the number of scintillators, which receive the scintillators in such a way that the scintillators are surrounded by walls of the compartments with the exception of their side respectively facing the photodiode arrangement.
 2. The radiation detector as claimed in claim 1, in which the compartments of the reflector part are arranged in a manner corresponding to the arrangement of the photodiodes in such a way, and the reflector part is arranged with respect to the photodiode arrangement in such a way, that a scintillator is in each case arranged opposite a photodiode of the photodiode arrangement.
 3. The radiation detector as claimed in claim 1 or 2, whose scintillators are fixed in the compartments of the reflector part by adhesive bonding.
 4. The radiation detector as claimed in one of claims 1 to 3, whose reflector part is of one-part design.
 5. The radiation detector as claimed in one of claims 1 to 4, whose reflector part is designed as an injection-molded or die-cast part.
 6. The radiation detector as claimed in one of claims 1 to 5, whose reflector part is formed from plastic.
 7. The radiation detector as claimed in claim 6, in which the plastic contains an optically reflective filler.
 8. The radiation detector as claimed in one of claims 1 to 7, whose reflector part and whose photodiode arrangement have, interacting with one another, centering means which, in the case of the arrangement of the reflector part and in front of the photodiode arrangement, ensure that the scintillators assume the defined positions relative to the photodiodes of the photodiode arrangement.
 9. The radiation detector as claimed in one of claims 1 to 8, which has a scattered radiation collimator with collimator plates which is arranged in front of the reflector part.
 10. The radiation detector as claimed in claim 9, whose reflector part having walls bounding the compartments and whose scattered radiation collimator have, interacting with one another, centering means which, in the case of the arrangement of the scattered radiation collimator and in front of the reflector part, ensure that the collimator plates of the scattered radiation collimator are aligned with walls of the reflector part which bound the compartments.
 11. The radiation detector as claimed in one of claims 1 to 10, which is composed of a plurality of modules, each of which comprises a reflector part with scintillators and a photodiode arrangement.
 12. The radiation detector as claimed in claim 11, in which each module has a scattered radiation collimator. 